Nickel-based superalloy having very high resistance to hot-corrosion for monocrystalline blades of industrial turbines

Abstract

Nickel-based superalloy, suitable for monocrystalline solidification, having the following composition by weight: Co: 4.75 to 5.25%Cr: 15.5 to 16.5%Mo: 0.8 to 1.2%W: 3.75 to 4.25%Al: 3.75 to 4.25%Ti: 1.75 to 2.25%Ta: 4.75 to 5.25%C:0.006 to 0.04%B:≦0.01%Zr:≦0.01%Hf:  ≦1%Nb:  ≦1%Ni and any impurities:complement to 100%.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S) [0001] This application is a continuation of U.S. application Ser. No. 10 / 460,860, filed Jun. 12, 2003, which is a continuation of U.S. application Ser. No. 09 / 999,167, filed Nov. 29, 2001, which claims priority of European Patent Application Number EP00403361, filed Nov. 30, 2000.TECHNICAL FIELD [0002] The invention relates to a nickel-based superalloy which is adapted to the manufacture of fixed and movable monocrystalline blades of industrial gas turbines by directional solidification. BACKGROUND OF THE INVENTION [0003] Nickel-based superalloys are the most high-performance materials used today in the manufacture of movable and fixed blades of industrial gas turbines. The two principal features required until now of these alloys for those specific applications have been good resistance to creep at temperatures of up to 850° C. and very good resistance to hot-corrosion. Some reference alloys currently used in this field are designated IN73...

AI Technical Summary

Benefits of technology

[0014] Furthermore, this superalloy must demonstrate good micro-structural stability in respect of the precipitation of fragile intermetallic phases which are rich in chrome when maintained for sustained periods at elevated temperature.

[0021] a density which is less than 8.4 g·cm−3 in order to minimize the mass of the monocrystalline blades and, consequently, to limit the centrifugal stress acting on the blades and on the turbine disc to which they are fixed;

[0022] a good tendency to monocrystalline solidification of turbine blades whose height can reach several tens of centimeters and the mass several kilograms.

Problems solved by technology

The same type of problem has been posed in the past in the case of gas turbines for turbo-jets and turbo-engines for aeronautical applications.

Furthermore, the process of monocrystalline solidification allows the preferred orientation of growth of the monocrystalline component to be selected and, that manner, the orientation which is optimum from the point of view of resistance to creep and thermal fatigue to be chosen, those two types of mechanical stress being the most disadvantageous for turbine blades.

However, the chemical superalloy compounds developed for monocrystalline turbine blades for aeronautical applications are not suitable for blades for terrestrial or marine applications, known as industrial applications.

In very severe environments, which are representative of extreme operating conditions, it has been shown that the resistance to hot-corrosion of that alloy remained inferior to that of alloy IN738.

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